Incidence of indicator organisms, opportunistic and pathogenic bacteria in fish

Abstract

Fish is an excellent source of high quality protein; however, it is susceptible to microbial spoilage. Fish carries high microbial load on the surface of the skin, in the intestine and in the gills. In Botswana, fishermen catch fish and sell their products in the open market. The microbiological quality and safety of these street vended fish have always been contentious. Therefore, a study on fish sold in Gaborone, Botswana was conducted from July 2006 to January 2007. Tilapia from the supermarkets and tilapia and catfish from street vendors were analyzed for the microbial load, presence of indicator microorganisms, opportunistic and pathogenic bacteria using conventional microbiological methods. Though coliforms were found in 84% of fish from the street vendors, only 16% of the fish had coliforms above the acceptable limits (3 log10 CFU/g). No Escherichia coli were isolated. Bacteria which are associated with plants, animals and soils but are normally classified as coliforms because of their biochemical reactions to sugars such as Citrobacter species, Klebsiella species including the enteropathogen Salmonella species were isolated. Fresh water or tap water is not available where vendors degut the fish. Hence, they carry water in containers to the point of sale sites and use it repeatedly. The unsanitary water (8.7 log10 CFU/ml of bacteria) used during the gutting of tilapia on the streets influenced the microbial levels in the fish, which were 6.0 log10 CFU/g compared to the 3.90 log10 CFU/g of ungutted whole tilapia from the same sale points. Frozen tilapia from supermarkets also had high bacterial counts (4.8 log10 CFU/g). Staphylococcus species were isolated frequently in all fish analyzed. Salmonella arizonae, Salmonella paratyphi (22-40%) was only isolated in street vended fish. Other bacterial isolates from fish included Citrobacter brackii, Citrobacter freundii, Enterobacter sakazakii, Enterobacter cloacae, Vibrio cholorae, Proteus mirabilis, Proteus vulgaris, Klebsiella pneumoniae and Aeromonas hydrophila. The presence of diverse enteric bacteria indicated the degree of cross contamination from the handlers. Their presence represents a potential hazard to humans, especially the immunocompromised consumers such as cases of HIV/AIDS. Stringent regulations on registration of fishermen, traders, education and mandatory observance of sanitation at trading points and use of ice have to be enforced to ensure safety of fish consumption.

Key words: Indicator bacteria, pathogens, tilapia, catfish